EP0411207A2 - Digital receiver operating at sub-nyquist sampling rate - Google Patents
Digital receiver operating at sub-nyquist sampling rate Download PDFInfo
- Publication number
- EP0411207A2 EP0411207A2 EP89121207A EP89121207A EP0411207A2 EP 0411207 A2 EP0411207 A2 EP 0411207A2 EP 89121207 A EP89121207 A EP 89121207A EP 89121207 A EP89121207 A EP 89121207A EP 0411207 A2 EP0411207 A2 EP 0411207A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- frequency
- subcarrier
- signal
- sampling
- composite signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
- H03D1/00—Demodulation of amplitude-modulated oscillations
- H03D1/22—Homodyne or synchrodyne circuits
- H03D1/2245—Homodyne or synchrodyne circuits using two quadrature channels
- H03D1/2254—Homodyne or synchrodyne circuits using two quadrature channels and a phase locked loop
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/16—Circuits
- H04B1/1646—Circuits adapted for the reception of stereophonic signals
Definitions
- the present invention relates to digital data receivers, and more particularly relates to digital receivers that can digitally recover data by sampling at sub-Nyquist sampling rates.
- the present invention is described with reference to one particular application thereof, namely a system for recovering digital subcarrier data from a conventional FM broadcast signal. It should be recognized, however, that the invention is not so limited.
- Subcarriers on FM broadcast signals are increasingly being used to transmit digital data to subscribers of subcarrier data services.
- Data being transmitted by such services includes stock market reports and paging information.
- a subcarrier-based paging system is disclosed in U.S. Patent 4,713,808 to Gaskill, the disclosure of which is incorporated herein by reference.
- a continuous signal must be sampled at a frequency above the Nyquist rate if the signal is to be properly characterized.
- the Nyquist rate is defined as twice the signal's highest frequency.
- frequency aliasing results, causing various portions of the signal's spectrum to interfere with each other. If this interference is uncontrolled, the signal can be lost or scrambled. That is, the sampled data may correspond to two or more different input signals. To avoid this possibility, most digital systems sample at rates well in excess of the Nyquist rate.
- the sampling problem was avoided by using phase shift keying.
- the data modulating the subcarrier was recovered at the wristwatch receiver by noting whether the subcarrier was in phase or out of phase with the pilot signal. This detection of the subcarrier phase was performed at a 19 KHz rate.
- phase shift keying method was advantageous in certain respects, it required a subcarrier bandwidth of 38 KHz to achieve a 19 Kbit transmission rate - an inefficient use of spectrum. Modulation of the subcarrier using amplitude modulation would have permitted more efficient use of the spectrum, but would have required sampling at a rate in excess of the Nyquist criteria - a feat difficult to achieve given the constraints associated with the wristwatch design.
- an object of the present invention to circumvent the Nyquist sampling criteria. More particularly, it is an object of the present invention to permit a digital receiver to sample an amplitude modulated subcarrier at sub-Nyquist rates in a manner that controls the frequency aliasing such that the aliasing produces a constructive interference between the upper and lower sidebands.
- this object is achieved in the present invention by sampling the amplitude modulated subcarrier synchronously to its carrier.
- sampling the signal at the times when the subcarrier is at its peak values, the data signal can be recovered at less than the Nyquist rate.
- Sampling is synchronized to the subcarrier by generating a sampling clock from a synchronizing signal transmitted with the modulated carrier that is phase locked thereto.
- a typical FM signal is composed of several components, as shown in Fig. 1. Principal among these are the audio subbands.
- the left plus right channel audio is broadcast in a first subband extending from 0 to about 15 KHz.
- the left minus right channel audio is broadcast in a second subband extending from about 23 to 53 KHz. Between these two audio bands is a stereo pilot signal at 19 KHz.
- Subcarrier data is typically transmitted in the portion of the spectrum above 53 KHz.
- the subcarrier is at 66.5 KHz and is amplitude modulated with 19 KHz data. This 19 KHz modulation spreads the subcarrier signal from 57 to 76 KHz.
- the majority of the signal power is concentrated in the audio subbands.
- the subcarrier typically represents one percent or less of the transmitted power.
- an illustrative data receiver 10 includes an antenna 12, a front end 14 and a data decoder 16.
- the antenna 12 receives RF FM broadcast signals and provides them to the front end 14.
- the front end 14 converts these signals to baseband and provides the baseband signal spectrum to the data decoder 16.
- the data decoder recovers the data signals from the baseband spectrum and provides output signals corresponding thereto to a user interface 18.
- the data decoder 16 includes a frequency source 20 that generates a 133 KHz low duty cycle sampling clock signal which is phase locked to the 19 KHz stereo pilot signal.
- This phase locked frequency source 20 includes a voltage controlled oscillator 22, a frequency divider 24, a multiplier 26 and a low pass filter 28.
- the voltage controlled oscillator 22 operates nominally at 133 KHz.
- the frequency divider 24 divides the 133 KHz signal output from the oscillator by seven to yield a 19 KHz signal. This signal is mixed with the 19 KHz pilot signal from the composite FM signal by the mixer 26.
- the mixer output includes a low frequency difference term that represents a phase error between the voltage controlled oscillator output and the 19 KHz stereo pilot signal.
- This low frequency signal is filtered from all the other mixer products by the low pass filter 28 and is applied in a feedback loop back to the oscillator 22 to correct its frequency.
- the loop thus operates to lock the phase of the 133 KHz oscillator 22 to the phase of the stereo pilot signal.
- the 66.5 KHz subcarrier is itself generated from the 19 KHz stereo pilot by a phase locked frequency multiplier circuit. Consequently, the 133 KHz sampling clock produced by the frequency source 20 is phase locked to the 66.5 KHz subcarrier being decoded.
- the radio station also includes provision for adjusting the phase offset between the 19 KHz pilot signal and the 66.5 KHz subcarrier so that the receiver of the present invention samples at the peaks of the subcarrier waveform.
- the 133 KHz sampling clock in the Fig. 2 embodiment is used to periodically trigger an analog sample and hold circuit 30, which operates in conjunction with an analog storage device, such as a capacitor 32.
- the sampled analog signal produced thereby is converted into digital form, again at the 133 KHz rate, by an analog-to-digital converter 34.
- These digital samples are applied to a 32 element finite impulse response digital filter 36 that passes the 66.5 KHz modulated subcarrier and attenuates the entertainment programming portions of the baseband FM spectrum.
- the resulting signal output from the filter 36 contains just the subcarrier portion of the baseband spectrum, sampled at a 133 KHz rate. This data is decoded and the resulting output signals applied to the user interface 18.
- each zero crossing of the carrier signal forces a zero crossing in the composite baseband signal. Since the times of the zero crossings of the baseband signal are known, its maxima and minima can be accurately approximated as the points midway between the zero crossings. Since the sampling clock is phase locked to the subcarrier frequency, it can sample, reliably, at approximately these mid points. This sampling at known maxima and minima is graphically illustrated in Fig. 3. Since the signal maxima and minima can be accurately determined, the modulating signal can readily be recovered, despite non-compliance with the Nyquist criteria.
- Fig. 4 shows a portion of another form of the present invention in which the phase locking circuitry is implemented in digital form, using a numerically controlled oscillator, a digital low pass filter, etc.
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
- Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
- Synchronisation In Digital Transmission Systems (AREA)
- Circuits Of Receivers In General (AREA)
Abstract
Description
- The present invention relates to digital data receivers, and more particularly relates to digital receivers that can digitally recover data by sampling at sub-Nyquist sampling rates.
- For expository convenience, the present invention is described with reference to one particular application thereof, namely a system for recovering digital subcarrier data from a conventional FM broadcast signal. It should be recognized, however, that the invention is not so limited.
- Subcarriers on FM broadcast signals are increasingly being used to transmit digital data to subscribers of subcarrier data services. Data being transmitted by such services includes stock market reports and paging information. A subcarrier-based paging system is disclosed in U.S. Patent 4,713,808 to Gaskill, the disclosure of which is incorporated herein by reference.
- It is well known that a continuous signal must be sampled at a frequency above the Nyquist rate if the signal is to be properly characterized. (The Nyquist rate is defined as twice the signal's highest frequency.) If a sub-Nyquist rate is used, frequency aliasing results, causing various portions of the signal's spectrum to interfere with each other. If this interference is uncontrolled, the signal can be lost or scrambled. That is, the sampled data may correspond to two or more different input signals. To avoid this possibility, most digital systems sample at rates well in excess of the Nyquist rate.
- In many applications, it is desirable to sample a signal at less than the Nyquist rate. By so doing, the system's cost and power consumption are reduced, and its hardware complexity is simplified. One such application is the paging system described in the Gaskill patent referenced above, in which the receiver is implemented in wristwatch form.
- In the modulation system originally described in the Gaskill patent, the sampling problem was avoided by using phase shift keying. The data modulating the subcarrier was recovered at the wristwatch receiver by noting whether the subcarrier was in phase or out of phase with the pilot signal. This detection of the subcarrier phase was performed at a 19 KHz rate.
- While the phase shift keying method was advantageous in certain respects, it required a subcarrier bandwidth of 38 KHz to achieve a 19 Kbit transmission rate - an inefficient use of spectrum. Modulation of the subcarrier using amplitude modulation would have permitted more efficient use of the spectrum, but would have required sampling at a rate in excess of the Nyquist criteria - a feat difficult to achieve given the constraints associated with the wristwatch design.
- To permit use of an amplitude modulated subcarrier in the Gaskill system, it is an object of the present invention to circumvent the Nyquist sampling criteria. More particularly, it is an object of the present invention to permit a digital receiver to sample an amplitude modulated subcarrier at sub-Nyquist rates in a manner that controls the frequency aliasing such that the aliasing produces a constructive interference between the upper and lower sidebands.
- Briefly, this object is achieved in the present invention by sampling the amplitude modulated subcarrier synchronously to its carrier. By sampling the signal at the times when the subcarrier is at its peak values, the data signal can be recovered at less than the Nyquist rate. Sampling is synchronized to the subcarrier by generating a sampling clock from a synchronizing signal transmitted with the modulated carrier that is phase locked thereto.
- The foregoing and additional objects, features and advantages of the present invention will be more readily apparent from the following detailed description thereof, which proceeds with reference to the accompanying drawings.
-
- Fig. 1 is a diagram showing the composite baseband spectrum of an FM broadcast signal that includes an amplitude modulated subcarrier.
- Fig. 2 is a schematic block diagram of a subcarrier data receiver according to one embodiment of the present invention.
- Fig. 3 is a diagram showing the sampling of a 66.5 KHz amplitude modulated subcarrier at a rate of 133 KHz according to one embodiment of the present invention.
- Fig. 4 is a schematic block diagram of a subcarrier data receiver according to another embodiment of the present invention.
- Reviewing briefly, a typical FM signal is composed of several components, as shown in Fig. 1. Principal among these are the audio subbands. The left plus right channel audio is broadcast in a first subband extending from 0 to about 15 KHz. The left minus right channel audio is broadcast in a second subband extending from about 23 to 53 KHz. Between these two audio bands is a stereo pilot signal at 19 KHz.
- Subcarrier data is typically transmitted in the portion of the spectrum above 53 KHz. In the illustrated embodiment, the subcarrier is at 66.5 KHz and is amplitude modulated with 19 KHz data. This 19 KHz modulation spreads the subcarrier signal from 57 to 76 KHz.
- As illustrated in Fig. 1, the majority of the signal power is concentrated in the audio subbands. The subcarrier typically represents one percent or less of the transmitted power.
- Referring now to Fig. 2, an
illustrative data receiver 10 according to the present invention includes anantenna 12, afront end 14 and adata decoder 16. Theantenna 12 receives RF FM broadcast signals and provides them to thefront end 14. Thefront end 14 converts these signals to baseband and provides the baseband signal spectrum to thedata decoder 16. The data decoder recovers the data signals from the baseband spectrum and provides output signals corresponding thereto to auser interface 18. - In more detail, the
data decoder 16 includes afrequency source 20 that generates a 133 KHz low duty cycle sampling clock signal which is phase locked to the 19 KHz stereo pilot signal. This phase lockedfrequency source 20 includes a voltage controlledoscillator 22, afrequency divider 24, amultiplier 26 and alow pass filter 28. The voltage controlledoscillator 22 operates nominally at 133 KHz. Thefrequency divider 24 divides the 133 KHz signal output from the oscillator by seven to yield a 19 KHz signal. This signal is mixed with the 19 KHz pilot signal from the composite FM signal by themixer 26. The mixer output includes a low frequency difference term that represents a phase error between the voltage controlled oscillator output and the 19 KHz stereo pilot signal. This low frequency signal is filtered from all the other mixer products by thelow pass filter 28 and is applied in a feedback loop back to theoscillator 22 to correct its frequency. The loop thus operates to lock the phase of the 133KHz oscillator 22 to the phase of the stereo pilot signal. - At the FM transmitter, the 66.5 KHz subcarrier is itself generated from the 19 KHz stereo pilot by a phase locked frequency multiplier circuit. Consequently, the 133 KHz sampling clock produced by the
frequency source 20 is phase locked to the 66.5 KHz subcarrier being decoded. The radio station also includes provision for adjusting the phase offset between the 19 KHz pilot signal and the 66.5 KHz subcarrier so that the receiver of the present invention samples at the peaks of the subcarrier waveform. - The 133 KHz sampling clock in the Fig. 2 embodiment is used to periodically trigger an analog sample and hold
circuit 30, which operates in conjunction with an analog storage device, such as acapacitor 32. The sampled analog signal produced thereby is converted into digital form, again at the 133 KHz rate, by an analog-to-digital converter 34. These digital samples are applied to a 32 element finite impulse responsedigital filter 36 that passes the 66.5 KHz modulated subcarrier and attenuates the entertainment programming portions of the baseband FM spectrum. The resulting signal output from thefilter 36 contains just the subcarrier portion of the baseband spectrum, sampled at a 133 KHz rate. This data is decoded and the resulting output signals applied to theuser interface 18. - Conventional sampling theory dictates that a subcarrier centered at 66.5 KHz and extending up to 76 KHz must be sampled at a minimum frequency of 152 KHz (2 x 76 KHz) if the data therein is to be unambiguously recovered. More typical would be sampling at three times the highest frequency component, or 228 KHz. In the present invention, however, the lower sampling rate of 133 KHz can be used. This lower sample rate can be used in this instance because (a) the subcarrier modulation is symmetrical (i.e. double sideband); (b) the subcarrier is phase locked to the sampling clock; and (c) there are no signals present at multiples of N*133 + 66.5 KHz to be aliased into the subcarrier signal.
- The double sideband modulation means the baseband signal takes the form:
V(t) = M(t) * cos2πF₀t (1)
where:
M(t) is the modulation signal;
F₀ is the carrier frequency; and
cos2πF₀t is the carrier signal waveform. - Since these modulation and carrier terms are multiplied together, each zero crossing of the carrier signal forces a zero crossing in the composite baseband signal. Since the times of the zero crossings of the baseband signal are known, its maxima and minima can be accurately approximated as the points midway between the zero crossings. Since the sampling clock is phase locked to the subcarrier frequency, it can sample, reliably, at approximately these mid points. This sampling at known maxima and minima is graphically illustrated in Fig. 3. Since the signal maxima and minima can be accurately determined, the modulating signal can readily be recovered, despite non-compliance with the Nyquist criteria.
- Fig. 4 shows a portion of another form of the present invention in which the phase locking circuitry is implemented in digital form, using a numerically controlled oscillator, a digital low pass filter, etc.
- Having described and illustrated the principles of our invention with reference to a detailed description thereof, it will be apparent that the invention can be modified in arrangement and detail without departing from such principles. Accordingly, we claim as our invention all such embodiments as may come within the scope and spirit of the following claims and equivalents thereto.
- The features disclosed in the foregoing description, in the claims and/or in the accompanying drawings may, both, separately and in any combination thereof, be material for realising the invention in diverse forms thereof.
Claims (4)
a front end for converting the RF composite signal to a baseband composite signal;
a frequency source for producing a sampling clock signal;
means for phase locking said frequency source to the pilot signal in the baseband composite signal;
sampling means for sampling said composite signal at a rate determined by the sampling clock signal;
analog to digital conversion means for converting the samples produced by the sampling means into digital form;
digital filter means for digitally filtering said digitized samples to attenuate the non-subcarrier components thereof;
wherein said sampling clock signal has a frequency less than twice the maximum frequency of the modulated subcarrier.
the pilot signal has a frequency of 19 kilohertz;
the subcarrier signal has a carrier frequency of 66.5 kilohertz; and
the sampling clock signal has a frequency of 133 kilohertz.
deriving from said composite signal a reference frequency having a known relationship with the subcarrier frequency;
sampling the composite signal periodically at certain phase conditions of the reference frequency;
digitizing the sampled composite signal to yield digital data; and
filtering said digital data to attenuate the non-subcarrier components of the digitized composite signal;
wherein said sampling occurs at a frequency twice the subcarrier frequency.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US388186 | 1988-08-01 | ||
US07/388,186 US4893341A (en) | 1989-08-01 | 1989-08-01 | Digital receiver operating at sub-nyquist sampling rate |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0411207A2 true EP0411207A2 (en) | 1991-02-06 |
EP0411207A3 EP0411207A3 (en) | 1992-02-05 |
EP0411207B1 EP0411207B1 (en) | 1994-10-12 |
Family
ID=23533045
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP89121207A Expired - Lifetime EP0411207B1 (en) | 1989-08-01 | 1989-11-16 | Digital receiver operating at sub-nyquist sampling rate |
Country Status (7)
Country | Link |
---|---|
US (1) | US4893341A (en) |
EP (1) | EP0411207B1 (en) |
JP (1) | JPH02192251A (en) |
AT (1) | ATE112905T1 (en) |
CA (1) | CA2004248A1 (en) |
DE (1) | DE68918857T2 (en) |
ES (1) | ES2064419T3 (en) |
Cited By (2)
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US7945004B2 (en) | 2007-12-14 | 2011-05-17 | Motorola Mobility, Inc. | Method and apparatus for detecting a frequency band and mode of operation |
US8055222B2 (en) | 2008-12-16 | 2011-11-08 | Motorola Mobility, Inc. | Multiple protocol signal detector |
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GB2242800B (en) * | 1990-04-03 | 1993-11-24 | Sony Corp | Digital phase detector arrangements |
US5416806A (en) * | 1992-06-15 | 1995-05-16 | International Business Machines Corporation | Timing loop method and apparatus for PRML data detection |
DE4303387A1 (en) * | 1993-02-05 | 1994-08-11 | Blaupunkt Werke Gmbh | Circuit arrangement for decoding a multiplex signal in a stereo radio receiver |
JPH07162383A (en) * | 1993-12-07 | 1995-06-23 | Hitachi Denshi Ltd | Fm stereo broadcasting equipment |
US5610825A (en) * | 1994-11-08 | 1997-03-11 | Johnson; William J. | Method and apparatus for the display of digitized analog signal loss |
US5768374A (en) * | 1996-08-06 | 1998-06-16 | Transcrypt International | Apparatus and method for continuous scrambling while transmitting or receiving synchronization data |
US6295362B1 (en) * | 1998-01-20 | 2001-09-25 | General Instrument Corporation | Direct digital synthesis of FM signals |
US6694128B1 (en) | 1998-08-18 | 2004-02-17 | Parkervision, Inc. | Frequency synthesizer using universal frequency translation technology |
US6091940A (en) | 1998-10-21 | 2000-07-18 | Parkervision, Inc. | Method and system for frequency up-conversion |
US6061551A (en) | 1998-10-21 | 2000-05-09 | Parkervision, Inc. | Method and system for down-converting electromagnetic signals |
US7515896B1 (en) * | 1998-10-21 | 2009-04-07 | Parkervision, Inc. | Method and system for down-converting an electromagnetic signal, and transforms for same, and aperture relationships |
US6542722B1 (en) | 1998-10-21 | 2003-04-01 | Parkervision, Inc. | Method and system for frequency up-conversion with variety of transmitter configurations |
US6370371B1 (en) | 1998-10-21 | 2002-04-09 | Parkervision, Inc. | Applications of universal frequency translation |
US6061555A (en) | 1998-10-21 | 2000-05-09 | Parkervision, Inc. | Method and system for ensuring reception of a communications signal |
US6049706A (en) | 1998-10-21 | 2000-04-11 | Parkervision, Inc. | Integrated frequency translation and selectivity |
US7039372B1 (en) * | 1998-10-21 | 2006-05-02 | Parkervision, Inc. | Method and system for frequency up-conversion with modulation embodiments |
US6813485B2 (en) | 1998-10-21 | 2004-11-02 | Parkervision, Inc. | Method and system for down-converting and up-converting an electromagnetic signal, and transforms for same |
US7236754B2 (en) | 1999-08-23 | 2007-06-26 | Parkervision, Inc. | Method and system for frequency up-conversion |
US6560301B1 (en) | 1998-10-21 | 2003-05-06 | Parkervision, Inc. | Integrated frequency translation and selectivity with a variety of filter embodiments |
US6704549B1 (en) | 1999-03-03 | 2004-03-09 | Parkvision, Inc. | Multi-mode, multi-band communication system |
US6704558B1 (en) | 1999-01-22 | 2004-03-09 | Parkervision, Inc. | Image-reject down-converter and embodiments thereof, such as the family radio service |
US6879817B1 (en) * | 1999-04-16 | 2005-04-12 | Parkervision, Inc. | DC offset, re-radiation, and I/Q solutions using universal frequency translation technology |
US6873836B1 (en) * | 1999-03-03 | 2005-03-29 | Parkervision, Inc. | Universal platform module and methods and apparatuses relating thereto enabled by universal frequency translation technology |
US6853690B1 (en) * | 1999-04-16 | 2005-02-08 | Parkervision, Inc. | Method, system and apparatus for balanced frequency up-conversion of a baseband signal and 4-phase receiver and transceiver embodiments |
US7110444B1 (en) * | 1999-08-04 | 2006-09-19 | Parkervision, Inc. | Wireless local area network (WLAN) using universal frequency translation technology including multi-phase embodiments and circuit implementations |
US7693230B2 (en) | 1999-04-16 | 2010-04-06 | Parkervision, Inc. | Apparatus and method of differential IQ frequency up-conversion |
US7065162B1 (en) | 1999-04-16 | 2006-06-20 | Parkervision, Inc. | Method and system for down-converting an electromagnetic signal, and transforms for same |
US8295406B1 (en) | 1999-08-04 | 2012-10-23 | Parkervision, Inc. | Universal platform module for a plurality of communication protocols |
US7082171B1 (en) * | 1999-11-24 | 2006-07-25 | Parkervision, Inc. | Phase shifting applications of universal frequency translation |
US7292835B2 (en) * | 2000-01-28 | 2007-11-06 | Parkervision, Inc. | Wireless and wired cable modem applications of universal frequency translation technology |
US7010286B2 (en) * | 2000-04-14 | 2006-03-07 | Parkervision, Inc. | Apparatus, system, and method for down-converting and up-converting electromagnetic signals |
US7010559B2 (en) * | 2000-11-14 | 2006-03-07 | Parkervision, Inc. | Method and apparatus for a parallel correlator and applications thereof |
US7454453B2 (en) * | 2000-11-14 | 2008-11-18 | Parkervision, Inc. | Methods, systems, and computer program products for parallel correlation and applications thereof |
US7072427B2 (en) * | 2001-11-09 | 2006-07-04 | Parkervision, Inc. | Method and apparatus for reducing DC offsets in a communication system |
US7379883B2 (en) * | 2002-07-18 | 2008-05-27 | Parkervision, Inc. | Networking methods and systems |
US7460584B2 (en) | 2002-07-18 | 2008-12-02 | Parkervision, Inc. | Networking methods and systems |
US6942660B2 (en) * | 2002-11-19 | 2005-09-13 | Conmed Corporation | Electrosurgical generator and method with multiple semi-autonomously executable functions |
TWI280690B (en) * | 2003-03-18 | 2007-05-01 | Tdk Corp | Electronic device for wireless communications and reflector device for wireless communication cards |
GB0725111D0 (en) | 2007-12-21 | 2008-01-30 | Wolfson Microelectronics Plc | Lower rate emulation |
MX2020010810A (en) * | 2018-04-20 | 2021-01-08 | Ericsson Telefon Ab L M | Method and apparatus for energy efficient transmission and reception of a signal using aliasing. |
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US4688253A (en) * | 1986-07-28 | 1987-08-18 | Tektronix, Inc. | L+R separation system |
DE3832455A1 (en) * | 1988-01-07 | 1989-07-27 | Pioneer Electronic Corp | Selection method for received frequencies of an RDS receiver |
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US4757538A (en) * | 1986-07-07 | 1988-07-12 | Tektronix, Inc. | Separation of L+R from L-R in BTSC system |
-
1989
- 1989-08-01 US US07/388,186 patent/US4893341A/en not_active Expired - Lifetime
- 1989-11-16 EP EP89121207A patent/EP0411207B1/en not_active Expired - Lifetime
- 1989-11-16 ES ES89121207T patent/ES2064419T3/en not_active Expired - Lifetime
- 1989-11-16 DE DE68918857T patent/DE68918857T2/en not_active Expired - Lifetime
- 1989-11-16 AT AT89121207T patent/ATE112905T1/en not_active IP Right Cessation
- 1989-11-20 JP JP1299895A patent/JPH02192251A/en active Pending
- 1989-11-30 CA CA002004248A patent/CA2004248A1/en not_active Abandoned
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4688253A (en) * | 1986-07-28 | 1987-08-18 | Tektronix, Inc. | L+R separation system |
DE3832455A1 (en) * | 1988-01-07 | 1989-07-27 | Pioneer Electronic Corp | Selection method for received frequencies of an RDS receiver |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7945004B2 (en) | 2007-12-14 | 2011-05-17 | Motorola Mobility, Inc. | Method and apparatus for detecting a frequency band and mode of operation |
US8055222B2 (en) | 2008-12-16 | 2011-11-08 | Motorola Mobility, Inc. | Multiple protocol signal detector |
Also Published As
Publication number | Publication date |
---|---|
EP0411207B1 (en) | 1994-10-12 |
EP0411207A3 (en) | 1992-02-05 |
ATE112905T1 (en) | 1994-10-15 |
DE68918857T2 (en) | 1995-03-02 |
CA2004248A1 (en) | 1991-02-01 |
ES2064419T3 (en) | 1995-02-01 |
JPH02192251A (en) | 1990-07-30 |
US4893341A (en) | 1990-01-09 |
DE68918857D1 (en) | 1994-11-17 |
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